Influence of chronic kanamycin administration on basement membrane anionic sites in the labyrinth

Unlocking the Power of Exosomes for Crossing Biological Barriers in Drug Delivery

Since the 2013 Nobel Prize was awarded for the discovery of vesicle trafficking, a subgroup of nanovesicles called exosomes has been driving the research field to a new regime for understanding cellular communication. This exosome-dominated traffic control system has increased understanding of many diseases, including cancer metastasis, diabetes, and HIV. In addition to the important diagnostic role, exosomes are particularly attractive for drug delivery, due to their distinctive properties in cellular information transfer and uptake. Compared to viral and non-viral synthetic systems, the natural, cell-derived exosomes exhibit intrinsic payload and bioavailability. Most importantly, exosomes easily cross biological barriers, obstacles that continue to challenge other drug delivery nanoparticle systems. Recent emerging studies have shown numerous critical roles of exosomes in many biological barriers, including the blood–brain barrier (BBB), blood–cerebrospinal fluid barrier (BCSFB), blood–lymph barrier (BlyB), blood–air barrier (BAB), stromal barrier (SB), blood–labyrinth barrier (BLaB), blood–retinal barrier (BRB), and placental barrier (PB), which opens exciting new possibilities for using exosomes as the delivery platform. However, the systematic reviews summarizing such discoveries are still limited. This review covers state-of-the-art exosome research on crossing several important biological barriers with a focus on the current, accepted models used to explain the mechanisms of barrier crossing, including tight junctions. The potential to design and engineer exosomes to enhance delivery efficacy, leading to future applications in precision medicine and immunotherapy, is discussed.

Advances in research on labyrinth membranous barriers

Integrity of the membranous labyrinth barrier system is of critical importance, which promotes inner ear homeostasis and maintains its features. The membranous labyrinth barrier system is divided into several subsets of barriers which, although independent from each other, are interrelated. The same substance may demonstrate different permeability characteristics through different barriers and under different conditions, while different substances can have different permeability features even in the same barrier under the same condition. All parts of the membranous labyrinth barrier structure, including their morphology, enzymes and channel proteins, and theirs permeability characteristics under various physiological and pathological conditions are reviewed in this paper. Infections, noise exposure, ototoxicity may all increase permeability of the barriers and lead to disturbances in inner ear homeostasis.

Short-term functional and morphological changes in guinea pig cochlea following intratympanic application of Burow's solution

OBJECTIVES

Burow's solution, comprising aluminum sulfate and acetic acid, is an otic drug formulation applied to the tympanic cavity. We characterized the relationship between the auditory brain stem response (ABR) thresholds and the area of the capillary basement membrane anionic sites in the stria vascularis after the application of Burow's solution.

METHODS

We used cationic polyethylenimine (PEI) to observe changes in the capillary basement membrane anionic sites in the stria vascularis. Burow's solution was dropped directly onto the round window membrane and retained for 2 hours. The ABRs were recorded at 4, 8, and 20 kHz immediately before surgery and before decapitation. The cochlea was extirpated immediately or 2 days after the surgery and immersed in cationic PEI solution. The PEI distribution associated with the capillary basement membrane anionic sites was measured in the basal and third turns.

RESULTS

The ABR threshold shifts at 4, 8, and 20 kHz were significantly increased immediately after the surgery, whereas those at 4 and 8 kHz, but not at 20 kHz, had recovered 2 days after the surgery. Further, the PEI distribution was significantly decreased immediately after the surgery and had recovered 2 days after the surgery.

CONCLUSIONS

Although Burow's solution may cause an acetic low pH in the stria vascularis and a temporary ABR threshold shift at 4 and 8 kHz, the permanent ABR threshold shift at 20 kHz cannot be attributed to the acetic low pH.

Trafficking of systemic fluorescent gentamicin into the cochlea and hair cells

Aminoglycosides enter inner ear hair cells across their apical membranes via endocytosis, or through the mechanoelectrical transduction channels in vitro, suggesting that these drugs enter cochlear hair cells from endolymph to exert their cytotoxic effect. We used zebrafish to determine if fluorescently tagged gentamicin (GTTR) also enters hair cells via apically located calcium-sensitive cation channels and the cytotoxicity of GTTR to hair cells. We then examined the serum kinetics of GTTR following systemic injection in mice and which murine cochlear sites preferentially loaded with systemically administered GTTR over time by confocal microscopy. GTTR is taken up by, and is toxic to, wild-type zebrafish neuromast hair cells. Neuromast hair cell uptake of GTTR is attenuated by high concentrations of extracellular calcium or unconjugated gentamicin and is blocked in mariner mutant zebrafish, suggestive of entry via the apical mechanotransduction channel. In murine cochleae, GTTR is preferentially taken up by the stria vascularis compared to the spiral ligament, peaking 3 h after intra-peritoneal injection, following GTTR kinetics in serum. Strial marginal cells display greater intensity of GTTR fluorescence compared to intermediate and basal cells. Immunofluorescent detection of gentamicin in the cochlea also revealed widespread cellular labeling throughout the cochlea, with preferential labeling of marginal cells. Only GTTR fluorescence displayed increasing cytoplasmic intensity with increasing concentration, unlike the cytoplasmic intensity of fluorescence from immunolabeled gentamicin. These data suggest that systemically administered aminoglycosides are trafficked from strial capillaries into marginal cells and clear into endolymph. If so, this will facilitate electrophoretically driven aminoglycoside entry into hair cells from endolymph. Trans-strial trafficking of aminoglycosides from strial capillaries to marginal cells will be dependent on as-yet-unidentified mechanisms that convey these drugs across the intra-strial electrical barrier and into marginal cells.

Cochlear damage due to germanium-induced mitochondrial dysfunction in guinea pigs

This investigation addressed the effect of germanium dioxide (GeO(2))-induced mitochondrial dysfunction on hearing acuity. Guinea pigs were fed chow that contained 0%, 0.15%, or 0.5% GeO(2). The animals that were fed 0.5% GeO(2) for 2 months developed hearing impairment chiefly due to degeneration of stria vascularis and cochlear supporting cells, which exhibited electron-dense mitochondrial inclusions. Cytochrome c oxidase activity was decreased in the skeletal muscles and kidney, which also exhibited electron-dense mitochondrial inclusions. No apparent pathological changes were observed in the utricle, semicircular canal, or among the vestibular nerve fibers, or in the liver or heart. The untreated animals and those treated with 0.15% GeO(2) did not exhibit hearing impairment or pathological changes in any organs. These findings suggest that administration of 0.5% GeO(2) induces mitochondrial dysfunction in the stria vascularis and supporting cells in the cochlea, as in the skeletal muscles and kidney, thereby causing hearing impairment in the guinea pigs.

Autoimmune Mouse Antibodies Recognize Multiple Antigens Proposed in Human Immune-Mediated Hearing Loss

HYPOTHESIS

Autoimmune diseased mice with hearing loss will have autoantibodies against the various cochlear antigens proposed in clinical autoimmune inner ear disease.

BACKGROUND

Serum antibodies of patients with hearing loss recognize several proteins that are proposed as possible antigenic targets in the ear. This often leads to a clinical diagnosis of autoimmune inner ear disease, although it is not clear how these antibodies cause inner ear disease. Therefore, to better understand the relationship of autoantibodies and ear disease, an examination was made of serum autoantibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse with hearing loss. Similar antibody patterns in the mouse would provide an animal model in which to investigate potential autoimmune mechanisms of this clinical ear disorder.

METHODS

Sera from MRL/MpJ-Fas(lpr) autoimmune mice and normal C3H mice were tested by the enzyme-linked immunosorbent assay technique for reactivity against various reported cochlear antigens: heat shock protein 70 (bovine, human, bacterial), laminin, heparan sulfate proteoglycan, cardiolipin, and collagen types II and IV.

RESULTS

The autoimmune mouse sera showed significantly greater antibody reactivity against all of the antigens when compared with normal mouse sera.

CONCLUSIONS

Serum antibodies from autoimmune mice recognized several putative autoantigens reported for patients with hearing loss, suggesting that comparable antigen-antibody mechanisms might be operating. However, the recognition of multiple antigens did not identify any one as being the specific target in autoimmune hearing loss. The correlation of antibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse and human studies indicates this animal model should aid further investigations into potential cochlear antigens in autoimmune hearing loss.

Effect of noise exposure on blood-labyrinth barrier in guinea pigs

The influence of noise exposure on the endothelial transport system in the cochlea was investigated using cationic polyethyleneimine (PEI), since systemically administered PEI passes through the capillary endothelial cell and attaches to basal lamina (BL) anionic sites in the cochlea. Under general anesthesia, all guinea pigs were administered an intravenous injection of 0.5% PEI. Thirty minutes later, five animals were exposed to noise (10 kHz, broad band noise, 105 dB SPL) for 30 min, via speakers inserted into the external auditory canal. The remaining five animals (controls) were left without noise exposure for 1 h following PEI injection. All guinea pigs were then immediately sacrificed, and the bony labyrinths were removed. PEI distribution on the BL was assessed in the stria vascularis, spiral ligament, basilar membrane, spiral limbus and Reissner's membrane throughout the cochlea with transmission electron microscopy. Compared to control animals, PEI distribution in the noise-exposed animals was significantly increased in the strial vessels of the basal and second turns and in Reissner's membrane of all turns. In the spiral ligament, basilar membrane and spiral limbus, no significant difference in PEI distribution was observed between the control and noise-exposed animals. These findings indicate that noise exposure increases macromolecular transport in the stria vascularis but not in the spiral ligament, spiral limbus and basilar membrane and that systemically administered macromolecules are more readily transported to Reissner's membrane by noise exposure.

Proteoglycan arrays in the cochlear basement membrane

Indirect immunofluorescence and transmission electron microscopy were used to investigate the composition and assembly of proteoglycans in the basement membranes of the spiral limbus, basilar membrane, spiral ligament, Reissner's membrane, myelinated nerve fibers, and blood capillaries of the spiral ligament and stria vascularis in the chinchilla cochlea. Four types of basement membrane components: laminin, entactin/nidogen, type IV collagen and heparan sulfate proteoglycans were immunolocalized in all basement membranes in association with heparan sulfate proteoglycans. beta 1 and alpha 1 integrin subunits were also detected along these basement membranes. The concentration of the basement membrane-associated proteins and integrin subunits differed according to the adjacent cell type. Electron microscopy showed that all basement membranes, with exception of those of stria vascularis, consist of two layers: lamina lucida and lamina densa. In the stria vascularis only a homogeneous lamina densa was observed. Cuprolinic blue treatment revealed heterogeneity in the ultrastructure and arrangement of proteoglycans in the cochlear basement membranes. Proteoglycans of the subepithelial basement membrane in the spiral limbus and spiral ligament formed quasi-regular, linear arrays within the lamina lucida, or were located at both sides of the lamina densa in the basilar membrane and Reissner's membrane. In the basement membranes of nerve fibers, and capillaries in the spiral ligament and stria vascularis, proteoglycans were scattered throughout these basement membranes, but showed different concentration and ultrastructural appearance, which may be related to different filtration and mechanical properties. In the basilar membrane, PGs were located above and below the lamina densa. An additional layer of PGs below the lamina densa may function as increased mechanical support of organ of Corti by its interaction with underlying fibrillar collagen layer. In the stria vascularis capillaries, PGs were stained considerably less with Cuprolinic blue and were scattered through the lamina densa of the basement membrane compared to capillaries of spiral ligament. This observation is compatible with a higher permeability of the strial capillaries.

Effect of furosemide on basal lamina anionic sites in guinea pig labyrinth

The authors studied the effects of acute furosemide administration on the basal lamina (BL) anionic sites in the stria vascularis, ampullar crista, and endolymphatic sac by using cationic polyethyleneimine (PEI). Furosemide was intravenously administered to albino guinea pigs with normal Preyer's reflexes. After 20 minutes, the bony labyrinth was removed and processed for histologic evaluation. Under a transmission electron microscope, a marked enlargement of the intercellular spaces was observed in the stria vascularis. The PEI distribution decreased significantly on the capillary BL in the stria vascularis and on the subepithelial BL in the sensory, transitional, and dark cell areas. However, no significant change was observed on the capillary BL or the subepithelial BL in the endolymphatic sac. These findings suggest that acute furosemide administration severely alters the distribution of the anionic sites in the strial capillary BL and in the subepithelial BL in the ampullar crista, but not in the capillary BL or the subepithelial BL of the endolymphatic sac.

Development of blood-labyrinth barrier in the semicircular canal ampulla of the rat

Cationic polyethyleneimine (PEI) administered intravenously was transported to anionic sites on the capillary and subepithelial basal laminae (BL) in the vestibular labyrinth. Therefore, changes in the PEI distribution on the BL reflect changes in the transport system in the vestibular labyrinth. A 0.1% PEI solution was administered intravenously (7.5 ml/kg) to developing (1, 4, 7, 14 days after birth) and adult rats in order to investigate the development of the macromolecular transport in the ampulla of the semicircular canal as a function of age. After 1 h, the bony labyrinth was removed and embedded in Epoxy resin. Ultrathin sections of the ampulla were then examined with a transmission electron microscope. In the subepithelial BL in the dark cell area and capillary BL in the crista ampullaris, the PEI distribution in both 1- and 4-day-old rats was markedly increased compared to that in either 7-, 14-day or adult rats. In the sensory cells in 1-, 4-day or 7-day-old rats, PEI density and area was significantly greater than in the adult rats. These findings suggest that the macromolecular transport system in the developing rat ampulla becomes mature by 14 days after birth and that the maturation of its transport system in the ampulla is strongly associated with that in the stria vascularis.

Development of the blood-labyrinth barrier in the rat

Systemically administered cationic polyethyleneimine (PEI) passes through the capillary endothelial cell and attaches to anionic sites on the capillary basal lamina (BL). Thus, the distribution of PEI on the BL reflects the changes in the endothelial cell transport system. A 0.1% PEI solution was administered by intravenous injection (7.5 ml/kg) to developing (4, 7, 11, 14, 21 days after birth) and adult rats to evaluate the development of endothelial cell transport in the cochlear capillary as related to age. One hour later, the bony labyrinth was removed and embedded in Epoxy resin. Ultrathin sections of the cochlear lateral wall were then viewed with a transmission electron microscope. The distribution of PEI in the capillary BL in the stria vascularis of the 4-, 7- and 11-day-old rats was significantly greater compared to the adult rats. The distribution of PEI in the capillary BL in the spiral ligament of the 4- and 7-day-old rats was also significantly greater compared to the adult rats. These findings suggest that the endothelial cell transport is more robust in the developing rat cochlea and that the blood-labyrinth barrier becomes mature by 14 days after birth in rats.

Effects of chronic administration of kanamycin on the basement membrane anionic sites in the crista ampullaris of guinea pigs

The authors investigated the effects of chronic kanamycin (KM) administration on the basement membrane (BM) anionic sites in the ampulla by studying the binding of cationic polyethyleneimine (PEI). KM sulfate was administered intramuscularly to guinea pigs with normal Preyer's reflexes daily for 10 or 17 days. The PEI distribution was unchanged on the subepithelial BM in the dark cell region and on the capillary BM in the crista ampullaris. However, PEI binding decreased significantly on the subepithelial BM in the sensory cell and transitional cell regions of those guinea pigs administered KM for 17 days. In the sensory cell region, the PEI distribution did not recover until 6 weeks after KM treatment. Findings suggest that chronic administration of KM severely alters the number of subepithelial BM anionic sites in the sensory cell region.